Chelated aryl synthesis

We have found that the late metal congeners of this important compound class are easily synthesized and can be derivatized to yield aryl monocyclo-octatetraene lanthanide complexes if the metal is small (Er—Lu) and the ligand bulky and chelating. The synthesis of these compounds clears the way for comparative reactivity studies (with cyclopentadienyl lanthanide complexes) and allows investigations of fundamental chemical reactivity to be conducted for this ligand system. 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al.89 They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-Ws(diphenyl-phosphino)butane (dppb) and 1,1 -/ E(diphenylphospliino)fcrroccnc... 

A number of a-aryl-A-alkyl nitrones and contrast enhancement compositions, which can be used to make contrast enhancement layer photoresist composites (230, 231), and inhibitors of free radical polymerization of monomers in nonexposed regions of the photoresist layer at selective actinic radiation (232). Histidine was used as a catalyst in the synthesis of a, A-diaryl nitrones in situ (233). To study diphenylborate chelates with mono- and bidentate ligands, a series of hydroxyl-containing nitrones have been synthesized (Fig. 2.7) (234-237). 

Even the sterically hindered 2,6-disubstituted aryl iodide 443 is carbonylated smoothly to give 445. Alkyl iodide present in the alcoholic component 444 remains intact under the carbonylation conditions. This carbonylation reaction is a key reaction in the synthesis of zearalenone (446) [216]. Optimal conditions for technical synthesis of the anthranilic acid derivative 448 from bromide 447 has been studied, and it has been found that A-acetyl protection of 447, which has a chelating effect, is important [217]. Cheaply available chlorides are rather inert [13]. The carbonylation of chloride 449 in the presence of DBU and Nal gives the amide 450 [218],... 

Brunner and Fiirst[431 reported the synthesis of a series of optically active, extended chelate phosphines, one of which was derived from the reaction of 5-bromo-l,3-di(bor-neoxymethyl)benzene (69) and bis(dichlorophosphino)methane (70). Technically, the product (-)-l,l-bis 3, 5 -di(borneoxymethyl)phenyl]phosphino methane (71) is both a first tier P- and 1,3-aryl-branched dendrimer. Excluding distortions, the maximum distance between the P atom and the most distant H atom(s) is 11.9 A for the two-layer ligand 71. The Rh-catalyzed [Rh(cod)Cl]2) hydrogenation of (a)-/V-acetamidocinnamic acid in the presence of 71 afforded a disappointingly low [5.2 % ee (/ )] optical induction. 

The reaction of palladium reagents with amines, phosphines, and other organic ligands to produce chelated complexes with Pd-C bonds is the Cyclometalation reaction (equation 7). It has been used to synthesize thousands of complexes with Pd-alkyl and Pd-aryl bonds. These complexes are beginning to be used as very stable, high turnover number catalysts and as intermediates in the synthesis of complex natural products. The scope and limitations of this reaction are detailed in Section 8. 

The Murai reaction (Scheme 4), the replacement of an ortho-CH on an aromatic ketone by an alkyl group derived from a substrate olefin, is catalyzed by a variety of Ru complexes. This C bond formation occurs via chelate directed C-H bond activation (cyclometalation) in the first step, followed by alkene insertion into RuH and reductive elimination of the alkylated ketone. In a recent example of the use of a related cyclometalation in complex organic synthesis, Samos reports catalytic arylation (Suzuki reaction) and alkenylation (Heck reaction) of alkyl segments of a synthetic intermediate mediated by Pd(II). 

Selective lithiation of alkyl- or aryl-pyridines is the key to the synthesis of a range of new phosphinopyridine ligands, e.g., (5), (6), and a fused phosphinomethylpyridinoferrocene. A similar approach has been used in the synthesis of chelating phosphino-oxazoline ligands, e.g.,... 

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